The present invention relates to painting systems including water-wash paint spray booths ventilated by recirculating process air through the booth.
It is conventional to ventilate a paint spray booth with a relatively large volume of process air in order to maintain an acceptable working environment within the spray booth. Two of the largest costs of operating a spray painting facility are preconditioning fresh make-up air to the required standards or characteristics, temperature and humidity, e.g., for use in the spray booth and for decontaminating, i.e., removing volatile organic compounds (VOCs) from that portion of the process air discharged to the atmosphere after leaving the spray booth. A known practice to reduce the costs associated with preconditioning fresh make-up air entering, and removing VOCs from air exhausted from, a spray booth is to reduce the volume of entry and exit air required to be treated, while preserving total process air flow through the spray booth work area or place, by directing a large portion of the ventilating air back to the booth. In popular use are water wash paint spray booths that include a sheet of water for collecting over-sprayed paint and for converting isocyanates, resulting from use of polyurethane paints, to harmless urea. In these booths, the relative humidity may approach 100% causing serious difficulties for paint application. While it is known to address these difficulties by employing refrigeration-type dehumidification to lower the humidity of the fresh air entering and/or process air being recirculated to the spray booth, this manner of dehumidification is very expensive, complex and difficult to maintain.